Schoolboys as young as 12 could soon be offered protection against sexually transmitted diseases through free vaccine shots.

The government drug-buying agency Pharmac is assessing an application from the Ministry of Health to extend free Gardasil shots to boys.

The drug has been offered to girls for four years to cut genital wart rates and protect against cervical cancer. Experts say it looks to have been successful.

If Pharmac agrees, 12- to 20-year-old males will be eligible for a publicly-funded course of injections to immunise against some types of human papilloma virus (HPV). It will be recommended to those so young because research has shown one in five 13-year-olds has had sex.

The $8.7 million HPV vaccination programme caters for intermediate schoolgirls but Australia is rolling out a world-first, a $21 million immunisation drive to vaccinate 900,000 pre-teen and teenage boys with Gardasil.

Just over half of New Zealand's intermediate and secondary girls have had the Gardasil vaccination since 2008. Last year, 52 per cent of year-8 girls were immunised.

Since vaccination started, there has been a 66 per cent drop in genital warts in teen girls.

Immunisation Advisory Centre director Dr Nikki Turner said extending Gardasil to boys was about protecting them from sexual disease.

She said boys would be safeguarded against genital warts and other rarer but nastier cancers.

"The more people that are vaccinated, the less disease in circulation."

New Zealand Sexual Health Society spokeswoman Dr Nicky Perkins was surprised to hear of the application.

She said sexual health clinicians would fully support it.

"Because it's a sexually transmitted infection, vaccinating girls and not boys doesn't make sense. We need to be vaccinating boys as well," said Perkins.

The drug has been available to Kiwi boys, but the $420 cost for the three injections means only a small percentage have opted for it.

The uptake of Gardasil in Kiwi girls has not been as good as clinicians wanted, and a vociferous anti-vaccination lobby was blamed.

Opponents include the mother of an Upper Hutt teenager who died in 2009, six months after her final dose of Gardasil.

Rhonda Renata wrote on the anti-Gardasil website offtheradar.co.nz that her fit and healthy daughter Jasmine, 18, would still be alive if she had not undergone the immunisation.

"I just wish someone had warned me about Gardasil. My Jasmine would still be here with us."

Renata told an inquest last year that after the first Gardasil dose, her daughter developed pains, had a racing heart and became tired and irritable. The coroner is still to release his finding into the cause of death.

A Pharmac spokesman said the agency's immunology subcommittee had reviewed the ministry's application and the findings would be discussed at Pharmac's clinical committee meeting in May and notes from the meeting released in June.

This would be followed by an economic analysis to see how the benefits and costs stacked up against other drugs vying for the public purse.

The vaccination is also effective against preventing other types of disease including throat, tongue, tonsil, penile and anal cancers.

For 19 years, she has treated people with the physical and emotional effects of genital warts and other sexual diseases.

It's why her pre-teen son became one of the country's earliest vaccinated boys. "I didn't want my son to go through what my patients go through," said the mother of two, who did not want her surname used to protect her son.

Three injections cost $420 but she said it was the best option for him and his future partners.